1. Field of the Invention
The present invention relates to a moving table apparatus wherein a table can be moved in a two different directions from the first direction.
2. Description of the Related Art
An X-Y table designed to move in two directions which are perpendicular to each other is well known and generally includes a base, on which is mounted a first table serving as a first moving support, to move in, for example, a direction Y, and a second table mounted on the first table and serving as a second moving support, to move in a direction X, which is perpendicular to direction Y. The first table is movably supported on two rails laid on the base, by means of bearings which contact the rails, while the second table is movably supported likewise on two rails laid on the first table. Since the second table moves in the direction Y, while the first table which supports the second table is moving in the direction X, the second table moves after all in both the direction X and the direction Y.
Among other uses, an X-Y table such as is described above is used as an alignment apparatus for use in a probing machine which examines the electrical properties of semiconductor wafers. This alignment apparatus has a probe card and a plurality of probes suspended from the probe card, and is designed to move each wafer, with the probes electrically connected to the electrodes formed and arranged on the wafer in rows and columns.
The X-Y table is also used in, for example, a machine tool, for positioning a work piece.
Particularly, an X-Y table used as an alignment apparatus must be designed such that the first and second tables are moved exactly in two straight lines which cross at a predetermined angle. The conventional assembly technique does not suffice to assemble the components of the X-Y table to allow the first and second tables to move in said two straight lines. An adjusting technique needs to be applied to adjust the angle between the two straight lines.
To adjust the angle accurately, use is made of a plate which has a lattice pattern printed on it and which is fixed on the second table. (The plate is fixed on a chuck supported on the second table and holding a wafer, in the case where the X-Y table is used in a probing machine.) A person who is engaged in assembling the X-Y table moves the second table in the direction Y, while moving the first table in the direction X, thus moving the second table in both directions. He observes, through a microscope, how the two tables move, with reference to the lattice pattern printed on the plate. When he finds that the straight lines extending in the directions X and Y, in which the first and second tables have been moved, cross at an angle different from the predetermined one, he changes the positions of the components of the X-Y table, thereby adjusting the angle to the predetermined one.
More specifically, the person may adjust the angle in one of the following two alternative methods.
In the first method, the bolts fastening a support table supporting the second table to a main table, which form the first table jointly with the support table, are loosened, and the support table is moved relative to the main table, thereby to adjust the angle to the predetermined angle. The support table can be so moved since the holes cut in both the support table and the main table have a diameter far greater than that of the bolts.
In the second method, the positional relationship between two bearings for moving the first and second tables, respectively, is changed, thereby to adjust the angle to the predetermined angle.
In the first method, however, no reference is given for positioning the support table. The support table may be moved in all directions, making it difficult to adjust the angle correctly.
With the second method, it is difficult to determine how much either bearing must be moved to adjust the angle to the desired extent. In addition, it is necessary to adjust the position of the magnet for attracting the bearing to a rail. The second method is complex and difficult.